The contemporary definition of interoception is not synonymous with the term “visceroception.” Visceroception refers to the perception of bodily signals arising specifically from the viscera: the heart, lungs, stomach, and bladder, along with other internal organs in the trunk of the body.[7] This does not include organs like the brain and skin. Interoception encompasses visceral signaling, but more broadly relates to all physiological tissues that relay a signal to the central nervous system about the current state of the body.[8] Interoceptive signals are transmitted to the brain via multiple pathways including (1) the lamina I spinothalamic pathway, (2) the classical viscerosensory pathway, (3) the vagus nerve and glossopharyngeal nerve, (4) chemosensory pathways in the blood, and (5) somatosensory pathways from the skin.

Interoception received increased visibility in the 21st century, but the concept was originally introduced by the Nobel Laureate Sir Charles S. Sherrington in 1906. Sherrington referred to interoception (although never stating the term, using “interoceptive” instead[12]) as a way to describe receptors in the body based on their location and function. Here, interoception was confined to the viscera, excluding all receptors and information from the body that would have been considered “exteroceptive” or “proprioceptive.” In Sherrington’s model, exteroceptive receptors received information from outward stimuli, like light, touch, sound, and odor. He classified temperature and nociception as exteroceptive sensations as well; however, these have now been regarded as having interoceptive qualities.[2][8] He further divided the internal milieu of the body by its somatic and autonomic functions. Here, proprioceptors were localized to skeletal tissue, which control voluntary movement. Interoceptors, a term which has lost prevalence in modern literature, were thus confined to visceral involuntary smooth muscle (e.g. surrounding blood vessels).[13]

Many experiments were conducted in the 1950s and 1960s regarding interoceptive processing. However, research did not start immediately after Sherrington’s discussion of interoceptors because a book by John Newport Langley was published stating that the autonomic nervous system only used efferent (brain-to-body) signaling to implement its functions.[14] This narrowed perspective halted research on interoceptive receptors for many years.[15] Once it became apparent that interoceptive receptors are present in many tissues of the body other researchers began to investigate afferent body-to-brain signals, mainly by conducting animal experiments to see if interoceptive conditioning was possible. Using principles of Pavlovian conditioning, different physiological systems in dogs were perturbed to elicit a conditioned response to food,[15] for example, in one experiment, dogs’ pelvises were distended using infusions of solution when food was presented to them. After rounds of pairing the two, salivation occurred without presenting food once the pelvis was distended.[15] Interoceptive conditioning studies like this illustrated that interoceptive sensations may be important for learned behavior and emotion.[15]

This graph shows the number of articles that reference the term “interoception” specifically from 1905 to 2015. A clear increase in the number of publications per year on the topic is seen in the 21st century.

The late 1950s and the 1960s saw an increased interest in interoception based on the number of publications released during that time period that referenced the term, this increase has been referred to as the “biofeedback blip,” where researchers examined the ability of a person to gain control over autonomic functions as a method of treatment for varying conditions.[16]

Interoception did not gain widespread popularity within the scientific community until the mid- to late-twentieth century, some researchers chose to use the term visceroceptor and interoceptor interchangeably, in line with Sherrington’s definition of the term;[15] some combined proprioceptive and visceroceptive information into one category - interoception - based on physiological data about the lack of differences in nerve impulses,[17][18] and some proposed that interoception is composed of more than just endogenous (internal) stimuli.[12] There is ongoing debate about which sensory signals could or should be classified as "interoceptive."

During the 1980s, psychophysiologists began to examine cardiovascular interoception extensively, introducing several different tasks for studying heartbeat perception: heartbeat counting,[9] heartbeat tapping,[19] and heartbeat detection.[20][21]Psychiatrists were also beginning to look at the effects of pharmacological stimulation on panic disorder symptoms as well.[22] This led to a growing interest in interoception during this time period, including the development of theoretical models on the integration of interoceptive information within the body over time.[23]

The twenty-first century has seen an exponential increase in publications on the topic of interoception, and a recognition of the multifaceted nature of this concept,[1] with a renewed interest in research, different ideas about interoception have emerged. One definition widens the concept to encompass “the skin and all that is underneath the skin” and the perception and function of bodily activity[3] to more fully understand psychosomatic processes;[8] in a similar vein, neuroanatomists hoping to find the anatomical basis of interoceptive functioning have stated the existence of a homeostatic pathway from the body to the brain that represents “the physiological status of all tissues in the body” and that this mapping onto the brain provides an individual with subjective feeling states which are critical for human emotion and self-awareness.[2]

For example, interoception is the fundament of the modern view on allostasis and allostatic load, the regulatory model of allostasis claims that the brain’s primary role as an organ is the predictive regulation of internal sensations. Predictive regulation refers to the brain’s ability to anticipate needs and prepare to fulfill them before they arise.[24] Therefore, in this model, the brain is responsible for efficient regulation of its internal milieu.

Interoception is sometimes generally referred to as “the perception of internal body states”[10] although there are many interoceptive processes in the body which are not perceived. Importantly, interoception is made possible through a process of “integrating the information coming from inside the body into the central nervous system.”[25] This definition deviates from Sherrington’s original proposition, but exemplifies the dynamic and widening breadth of interoception as a concept in modern literature.

This table defines many of the different facets or components of interoception.

Although interoception as a term has more recently gained increased popularity, different aspects of it have been studied since the 1950s, these include the features of attention, detection, magnitude, discrimination, accuracy, sensibility, and self-report.[1][26] Despite not using the word “interoception” specifically, many publications in the physiology and medical fields have focused on understanding interoceptive information processing in different organ systems. Attention describes the ability to observe sensations within the body, it can be directed voluntarily in a "top down" manner or it can be attracted involuntarily in a "bottom up" manner. Detection reflects the presence or absence of a conscious report of interoceptive stimuli, like a heartbeat or growling stomach. Magnitude is the intensity of the stimulus, or how strongly the stimuli is felt. Discrimination describes the ability to localize interoceptive stimuli in the body to specific organs and differentiate them from other bodily stimuli that also occur, like distinguishing between a heart which is beating hard from an upset stomach. Accuracy (or sensitivity) refers to how precisely and correctly an individual can monitor specific interoceptive processes. Self-report is itself multifaceted, it describes the ability to reflect on interoceptive experiences occurring over different periods of time, make judgments about them, and describe them. Although all of these components of interoception have been studied since the mid-twentieth century, they have not been brought together under the umbrella-term “interoception” until more recently,[1] the term "interoceptive awareness" is also frequently used to encompass any (or all) of the different interoception features that are accessible to conscious self-report. This multifaceted approach offers a unified way of looking at interoceptive functioning and its different features, it clarifies the definition of interoception itself, and it informs structured ways of assessing interoceptive experiences in an individual.

This graph shows the number of articles published on interoception vs. articles published on interoceptive facets without directly referencing the term from 1905-2015. The timeline starts one year before the publication of Charles Sherrington’s book, “The integrative action of the nervous system,” which introduced “interoception."[1]

This table illustrates the most common tasks that are used to assess cardiovascular interoception, broken down by the corresponding facets that they test. The exemplars at the bottom refer to specific studies or researchers who developed the task.[1]

Cardiac interoception has been widely studied as a method of evaluating interoceptive sensation, this is done using different tasks including heartbeat counting,[9] heartbeat tapping,[19] heartbeat detection[27][28] and heartbeat attention[29][30] tasks. Heartbeat counting tasks ask participants to count the number of felt heartbeats during short time periods, their reported count is then compared with the actual count obtained with an electrocardiogram. This measures the participant’s attention to his or her own heartbeat, the accuracy with which that is perceived, and the ability of the participant to report that measurement; however, results can be influenced by the participant’s preexisting knowledge of his or her heart rate[31][32] and an insensitivity to heart rate change.[33] Heartbeat detection tasks work by providing a participant with a musical tone which is played simultaneously or non-simultaneously with one’s heartbeat, asking the participant to report whether it is simultaneous or not with the tones. Heartbeat detection is commonly used because of its ability discern an individual’s performance above chance levels, so-called "good detectors." However, such detection rates among participants for this task are usually only 35%.[1] It also measures the participant’s attention, detection, discrimination, accuracy and self-report of the interoceptive process.[1] Heartbeat attention tasks are the most minimalistic, and involve simply the top-down direction of attention towards an interoceptive sensation such as the heartbeat, breath, or stomach.[29] Most perceptions of heartbeat sensations usually occur during a time of homeostatic perturbation, such as when the state of the body changes from external or internal influences such as physical exertion or elevated arousal states (e.g., riding a roller coaster, watching a scary movie, public speaking anxiety, or having a panic attack). For this reason, cardiac interoception is also sometimes studied by inducing perturbations of bodily state, this can be done pharmacologically using adrenaline-like drugs, such as isoproterenol, which mimics activation of the sympathetic nervous system,[10] resulting in increased heart rate and respiration rate, similar to the “fight-or-flight” response.[34][35] This approach provides a physiological basis for understanding psychiatric and neurological disorders that are characterized by heightened sympathetic nervous system activity.[10]

Respiratory perception can differ from other interoceptive physiological symptoms because of an individual’s ability to exert voluntary control over the system with controlled breathing or breathing exercises,[3] this system is often measured using restrictive breathing loads[36] and/or CO2 inhalation,[37] which are designed to mimic labored breathing sensations. Dyspnea, or difficulty breathing, is a commonly felt sensation associated with panic attacks; however, due to the voluntary control of breathing, this domain of interoception usually requires implementation of much more elaborate experimental controls to quantify in comparison to cardiac interoception.

Common interoceptive sensations related to the gastrointestinal and genitourinary systems are hunger and fullness, these are homeostatic signals that tell an individual when to eat and when to stop eating. The dorsal mid-insula appears to be integral in taste processing during gastrointestinal interoceptive attention tasks.[38] Rectal and bladder distensions are used as a method to perturb the homeostatic environment of the gastrointestinal and genitourinary systems, using placement of balloon catheters which can be inflated to achieve different stimulus intensities. Associative fear learning paradigms have been used to study how innocuous signals might lead to abnormal states of gastrointestinal hypersensitivity and anxiety.[39]Biofeedback therapy has been used for individuals with impaired gastrointestinal interoception, showing positive outcomes for some patients.[40]

Nociception refers to the receiving and processing of pain inducing stimuli by the central nervous system. Functional brain imaging studies during painful stimulation of the skin with heated probes, during mechanical compression, and electric shock have suggested that that the insular cortex is prominently activated during pain processing,[41] thus while pain was once thought of as an exteroceptive sensation, based on functional imaging and anatomical evidence it is now understood that it has an interoceptive component.

Temperature and pain are thought to be represented as “feelings” of coolness/warmness and pleasantness/unpleasantness in the brain, these sensory and affective characteristics of thermoregulation may motivate certain behavioral responses depending on the state of the body (for example, moving away from a source of heat to a cooler space). Such perturbations in the internal homeostatic environment of an organism are thought to be key aspects of a motivational process giving rise to emotional states, and have been proposed to be represented principally by the insular cortex as feelings.[5] These feelings then influence drives when the anterior cingulate cortex is activated.

The endocrine and immune systems are necessary body systems that aid in allostasis and homeostatic control. Imbalances in these systems, along with other genetic and social factors, may be linked to interoceptive dysregulation in depression,[42] these increased allostatic changes may cause a hyperawareness of interoceptive signaling and a hypo-awareness of exteroceptive signaling in depression patients.[43]

Soft touch refers to the stimulation of slow, unmyelinated C Tactile afferents. This is accompanied by a sense of pleasantness, and has been likened to other interoceptive modalities like thermoregulation and nociception because of the similarities in anatomical function.[44] Soft touch activates the insula rather than the somatosensory cortex, indicating that it has an affective importance absent in Aβ fibers, since soft touch utilizes a separate pathway, it may have a social relevancy, allowing the body to separate the “noise” of outward stimuli from stimuli that evokes an affective feeling.[44]

Multiple neural pathways relay information integral to interoceptive processing from the body to the brain. these include the lamina I spinothalamic pathway, the visceroceptive pathway, and the somatosensory pathway.

The lamina I spinothalamic pathway is commonly known for carrying information to the brain about temperature and pain, but it has been suggested to more broadly relay all information about the homeostatic condition of the body.[41]

Afferent signals enter the spinal cord at the superficial layer of the dorsal horn

Second order neurons cross the midline in the medulla, projecting up the opposite side and synapse on third order neurons in the ventral posterior lateral nucleus or ventromedial posterior nucleus of the thalamus

This image divides the insula into its anterior, mid, and posterior regions, with each being denoted by different colors.

The insula is critically involved in the processing, integration, and cortical representation of visceral and interoceptive information. Lamina I spinothalamic and vagal afferents project via the brainstem and thalamus to the posterior and mid dorsal insula respectively, from there, information travels to the posterior and mid-insula, which combines visceral and somatosensory information.[29] The insula is also activated during a variety of exteroceptive and affective tasks, the insula is considered to be a "hub" region because it has an extremely high number of connections with other brain areas, suggesting it may be important for an integration of lower-level physiological information and salience.[47]

The insula connects to many regions in the brain and is highly involved in many homeostatic functions.

The anterior insular cortex (AIC) is involved in the representation of “cognitive feelings” which arise from the moment-to-moment integration of homeostatic information from the body, these feelings engender self-awareness by creating a sentient being (someone able to feel and perceive) aware of bodily and cognitive processing.[41]

The insular cortex differs cytoarchitecturally based on its anterior, mid, and posterior regions. The posterior insular cortex is granular, the mid insular cortex is dysgranular (or slightly granulated) and the anterior insular cortex has no granulation whatsoever.

The insula contains three major subregions defined by the presence or absence of a granule cell layer: granular, dysgranular (slightly granulated) agranular, each of these portions of the insular cortex are important for different levels of functional connectivity. Information from the thalamus is projected to all three regions, those with increased granulation are considered to be capable of receiving sensory input.[4]

The anterior cingulate cortex (ACC) plays a significant role in motivation and the creation of emotion. An emotion can be seen as comprising both a feeling and a motivation based on that feeling. According to one view, the “feeling” is represented in the insula, while the “motivation” is represented in the ACC.[2] Many interoceptive tasks activate the insula and ACC together, specifically tasks that elicit strong aversive feeling states like pain.[48]

The sensory motor cortex provides an alternative pathway for sensing interoceptive stimuli, although not following the conventional pathway for interoceptive awareness, skin afferents which project to the primary and secondary somatosensory cortices provide the brain with information regarding bodily information. This area of the brain is commonly engaged by gastrointestinal distension and nociceptive stimulation, but it likely plays a role in representing other interoceptive sensations as well; in one study, a patient with bilateral insula and ACC damage was given isoproterenol as a method of exciting the cardiovascular system. Despite damage to putative interoceptive areas of the brain, the patient was able to perceive his heartbeat with similar accuracy compared to healthy individuals; however, once lidocaine was applied to the patient’s chest over the region of maximum cardiac sensation and the test was run again, the patient did not sense any change in heartbeat whatsoever.[49] This suggested that somatosensory information from afferents innervating the skin outside of the heart may provide information to the brain about the heart’s pounding through the somatosensory cortex.[49]

Disturbances of interoception occur prominently and frequently in psychiatric disorders, these symptom fluctuations are often observed during the most severe expression of dysfunction, and they figure prominently in diagnostic classification of several psychiatric disorders. A few typical examples are reviewed next.

Palpitations and dyspnea are hallmarks of panic attacks. Studies have shown that panic disorder patients report a heightened experience of interoceptive sensations, but these studies have failed to clarify whether this is simply due to their systematic bias toward describing such feelings.[54][55][56] However, other studies have shown that panic disorder patients feel heartbeat sensations more intensely when the state of the body is perturbed by pharmacological agents, suggesting they exhibit heightened sensitivity to experiencing interoceptive sensations.[1]

Functional neuroimaging studies have shown that posttraumatic stress disorder (PTSD) patients exhibit a decreased activation in the right anterior insula, a region of the brain that is largely responsible for identifying the mismatch between cognitive and interoceptive states.[57] Further, because PTSD patients have shown decreased activation within many nodes of the lamina I homeostatic pathway—a pathway through which the thalamus sends interoceptive information to the anterior insula and anterior cingulate—it has been suggested that PTSD patients experience reduced interoceptive awareness.[57]

The broad consensus of studies investigating the link between interoceptive awareness and anxiety disorders is that people with anxiety disorders experience heightened awareness of and accuracy in identifying interoceptive processes. Functional imaging studies provide evidence that people with anxiety disorders experience heightened interoceptive accuracy, suggested by hyperactivation in the anterior cingulate cortex—a region of the brain associated with interoception—in several different kinds of anxiety disorders,[58] the insula has been suggested to be abnormal in a large scale study across anxiety disorders in general.[59] Other studies have found that interoceptive accuracy is increased in these patients, as evidenced by their superior ability in heartbeat detection tasks in comparison to healthy controls.[60]

Anorexia nervosa (AN) has been associated with interoceptive disturbances. Patients with AN often develop insensitivity to interoceptive cues of hunger, and yet are highly anxious and report disturbed interoceptive experiences, both inside and out.[1] While AN patients concentrate on distorted perceptions of their body exterior in fear of weight gain, they also report altered physical states within their bodies, such as indistinct feelings of fullness,[61] or an inability to distinguish emotional states from bodily sensations in general (called alexithymia).[62][63]

Studies suggest that patients acutely suffering from bulimia nervosa (BN) exhibit heightened interoceptive accuracy, but that some patients who have recovered from the disorder show reduced interoceptive awareness under resting physiological conditions.[64] Further, BN patients consistently report reduced sensitivity to many other kinds of internal and external sensations, exhibiting increased thresholds to heat pain compared to healthy subjects[65] and an increased gastric capacity.[66] Neuroimaging literature suggests a pattern of heightened interoceptive awareness in patients with BN based on increased activity and volume in the insula and anterior cingulate cortex—regions associated with interoception and taste processing—when looking at food.[67]

Major depressive disorder (MDD) has been theoretically linked to interoceptive dysfunction. Studies have shown that women with MDD are less accurate on heartbeat counting tasks than are men with MDD[68] and that, in general, patients with MDD are less accurate at counting heartbeat than are patients with panic or anxiety disorders.[69] However, patients with MDD do not always exhibit reduced cardiac interoceptive accuracy; depressed patients experiencing high levels of anxiety will actually be more accurate on heartbeat detection tasks than depressed patients with lower levels of anxiety.[70]

Results from a study investigating the relationship between obsessive compulsive disorder (OCD) and internal body signals found that patients with OCD were more accurate on a heartbeat perception task than healthy controls and anxiety patients heightened interoceptive awareness.[73]

Patients with autism spectrum disorder (ASD) may have poorer interoceptive awareness than [control] subjects, it is hypothesized that this decrease in interoceptive accuracy is due to alexithymia, which is often associated with ASD.[74] However, it has also been found that children with ASD actually show greater interoceptive sensitivity than [control subjects] when measured over a long period of time.[74] Further investigation into the relationship between interoception and ASD is needed in order to fully understand the interoceptive aspect of the disorder.

The EPIC model proposes a method of understanding the brain’s response to stimuli contrary to the classic "stimulus-response" model, the classical view of information processing is that when a peripheral stimulus provided information to the central nervous system, it was processed in the brain, and a response was elicited. The EPIC model[4] deviates from this and proposes that the brain is involved in a process of active inference,[75][76] that is, assiduously making predictions about situations based on previous experiences. These predictions, when coupled with incoming sensory signals, allow the brain to compute a prediction error. Interoceptive prediction errors signal the occurrence of discrepancies within the body, which the brain attempts to minimize, this can be done by 1) modifying the predictions through brain-related pathways, 2) altering the body position/location in order to better align incoming sensory signals with the prediction, or 3) altering the brain’s method of receiving incoming stimuli.[4] Interoceptive prediction error signals are a key component of many theories of interoceptive dysfunction in physical and mental health.[77][78][79]

As attention on interoception increases among the scientific community, new research methods and treatment tactics are beginning to emerge. Ongoing research in interoception has shown the importance of perturbing interoceptive systems,[1] this allows researchers the ability to document the effects of non-baseline states, which occur during times of panic or anxiety. It also provides the participant the ability to gauge the intensity of sensations within the body, this can be done through pharmacological interventions, balloon distensions, or respiratory breathing loads depending on the interoceptive system of interest.

An open float pool

Another research method used to study interoception is specialized floatation environments.[80] Floating removes external stimuli so that individuals can more easily focus on the interoceptive sensations within their bodies. One idea with floating is that over many float sessions, patients with different kinds of disorders may learn to become more attuned or tolerant of their interoceptive sensations not only in the float tank but also in their everyday lives.[80]

Whole body hyperthermia may provide a new treatment technique for major depressive disorder,[81] it is thought that reducing one of the bodily symptoms of depression, which is increased inflammation, using whole body hyperthermia will also reduce depressive feelings represented in the brain. In theory, these techniques will help patients better attune themselves to their interoceptive sensations, allowing them a better understanding of what occurs in their bodies.

Meditation and mindfulness have been looked into as possible techniques to enhance interoceptive awareness based on their tendency to redirect focus within oneself. However, studies show that even though meditation and mindfulness practices promote attention to interoceptive sensations, they do not clearly increase interoceptive awareness in specific domains such as breath or body [null monitoring.][85][86]

Although a universal definition of interoception has not been reached, research on interoception and psychiatric disorders has shown a link between interoceptive processing and mental disorders, it has been proposed that exposure therapy, commonly used among anxiety disorders, may provide a basis for a model of interoceptive exposure therapy that could be incorporated into treatment plans of different psychiatric disorders.[1] One proposal states that multiple interoceptive challenges assessing different physiological systems could provide diagnosticians with the ability to create an “interoceptive profile” for a specific individual, creating a patient-specific treatment plan.[1]

^Kessler RC, Soukup J, Davis RB, et al. The Use of Complementary and Alternative Therapies to Treat Anxiety and Depression in the United States. American Journal of Psychiatry. 2001;158(2):289-294. doi:10.1176/appi.ajp.158.2.289.

1.
Sense
–
A sense is a physiological capacity of organisms that provides data for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology, the nervous system has a specific sensory system or organ, dedicated to each sense. Humans have a multitude of senses, sight, hearing, taste, smell, and touch are the five traditionally recognized senses. However, what constitutes a sense is a matter of debate, leading to difficulties in defining what exactly a distinct sense is. Other animals also have receptors to sense the world around them, humans have a comparatively weak sense of smell and a stronger sense of sight relative to many other mammals while some animals may lack one or more of the traditional five senses. Some animals may also intake and interpret sensory stimuli in different ways. Some species of animals are able to sense the world in a way humans cannot, with some species able to sense electrical and magnetic fields. There is no agreement as to the number of senses because of differing definitions of what constitutes a sense. The senses are frequently divided into exteroceptive and interoceptive, Exteroceptive senses are senses that perceive the bodys own position, motion, external senses include the traditional five, sight, hearing, touch, smell and taste, as well as thermoception and possibly an additional weak magnetoception. Proprioceptive senses include nociception, equilibrioception, proprioception, interoceptive senses are senses that perceive sensations in internal organs. Non-human animals may possess senses that are absent in humans, such as electroreception and detection of polarized light, in Buddhist philosophy, Ayatana or sense-base includes the mind as a sense organ, in addition to the traditional five. This addition to the commonly acknowledged senses may arise from the psychological orientation involved in Buddhist thought, the mind considered by itself is seen as the principal gateway to a different spectrum of phenomena that differ from the physical sense data. This way of viewing the human sense system indicates the importance of internal sources of sensation and perception that complements our experience of the external world, there are two types of photoreceptors, rods and cones. Rods are very sensitive to light, but do not distinguish colors, cones distinguish colors, but are less sensitive to dim light. There is some disagreement as to whether this one, two or three senses. Neuroanatomists generally regard it as two senses, given that different receptors are responsible for the perception of color and brightness, the inability to see is called blindness. Blindness may result from damage to the eyeball, especially to the retina, damage to the nerve that connects each eye to the brain. Temporary or permanent blindness can be caused by poisons or medications, people with blindsight are usually not aware that they are reacting to visual sources, and instead just unconsciously adapt their behaviour to the stimulus

2.
Insular cortex
–
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus. The insulae are believed to be involved in consciousness and play a role in diverse functions usually linked to emotion or the regulation of the bodys homeostasis and these functions include perception, motor control, self-awareness, cognitive functioning, and interpersonal experience. In relation to these, it is involved in psychopathology, the insular cortex is divided into two parts, the larger anterior insula and the smaller posterior insula in which more than a dozen field areas have been identified. The cortical area overlying the insula toward the surface of the brain is the operculum. The opercula are formed from parts of the frontal, temporal. The anterior part of the insula is subdivided by shallow sulci into three or four short gyri, the anterior insula receives a direct projection from the basal part of the ventral medial nucleus of the thalamus and a particularly large input from the central nucleus of the amygdala. In addition, the anterior insula projects to the amygdala. One study on rhesus monkeys revealed widespread reciprocal connections between the cortex and almost all subnuclei of the amygdaloid complex. The posterior insula projects predominantly to the aspect of the lateral. In contrast, the anterior insula projects to the anterior amygdaloid area as well as the medial, the cortical, the accessory basal magnocellular, the basal. The posterior part of the insula is formed by a long gyrus, the posterior insula connects reciprocally with the secondary somatosensory cortex and receives input from spinothalamically activated ventral posterior inferior thalamic nuclei. The same study revealed differences in the anatomical connection patterns between the left and right hemisphere, the circular sulcus of insula is a semi-circular sulcus or fissure that separates the insula from the neighboring gyri of the operculum in the front, above, and behind. The insular cortex has regions of cell structure or cytoarchitecture. The insula also receives differential cortical and thalamic input along its length, john Allman and his colleagues have shown that the anterior insular cortex contains a population of neurons, called spindle neurons. These are also called von Economo neurons, identified as characterising a distinctive subregion as the agranular frontal insula, the insular cortex is considered a separate lobe of the telencephalon by some authorities. Other sources see the insula as a part of the temporal lobe and it is also sometimes grouped with limbic structures deep in the brain into a limbic lobe. As a paralimbic cortex, the cortex is considered to be a relatively old structure. It has been speculated that these neurons are involved in processes that are specific to primates including great apes, such as empathy

3.
Somatosensory system
–
The somatosensory system is a part of the sensory nervous system. The somatosensory system is a system of sensory neurons and pathways that responds to changes at the surface or inside the body. The axons, of sensory neurons connect with, or respond to, sensory receptors are found all over the body including the skin, epithelial tissues, muscles, bones and joints, internal organs, and the cardiovascular system. Somatic senses are sometimes referred to as somesthetic senses, with the understanding that somesthesis includes the sense of touch, proprioception, the mapping of the body surfaces in the brain is called a cortical homunculus and plays a fundamental role in the creation of body image. This brain-surface map is not immutable, however, dramatic shifts can occur in response to stroke or injury. The four mechanoreceptors in the skin respond to different stimuli for short or long periods. Merkel cell nerve endings are found in the epidermis and hair follicles, they react to low vibrations. Due to a receptive field they are used in areas like fingertips the most, they are not covered. Tactile corpuscles react to moderate vibration and light touch and they are located in the dermal papillae, due to their reactivity they are primarily located in fingertips and lips. They respond in quick action potentials, unlike Merkel and they are responsible for the ability to read Braille and feel gentle stimuli. Lamellar corpuscles determine gross touch and distinguish rough and soft substances and they react in quick action potentials, especially to vibrations around 250 Hz. They are the most sensitive to vibrations, and have large receptor fields, pacinian reacts only to sudden stimuli so pressures like clothes that are always compressing their shape are quickly ignored. Bulbous corpuscles react slowly and respond to sustained skin stretch and they are responsible for the feeling of object slippage and play a major role in the kinesthetic sense and control of finger position and movement. Merkel and bulbous cells are myelinated, the rest are not, all of these receptors are activated upon pressures that squish their shape causing an action potential. All afferent touch/vibration info ascends the spinal cord via the posterior column-medial lemniscus pathway via gracilis or cuneatus, cuneatus sends signals to the cochlear nucleus indirectly via spinal grey matter, this info is used in determining if a perceived sound is just villi noise/irritation. All fibers cross in the medulla, the postcentral gyrus includes the primary somatosensory cortex collectively referred to as S1. BA3 receives the densest projections from the thalamus, bA3a is involved with the sense of relative position of neighboring body parts and amount of effort being used during movement. BA3b is responsible for distributing somato info, it projects texture info to BA1, region S2 divides into Area S2 and parietal ventral area

4.
Anterior cingulate cortex
–
The anterior cingulate cortex is the frontal part of the cingulate cortex that resembles a collar surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24,32, and 33 and it appears to play a role in a wide variety of autonomic functions, such as regulating blood pressure and heart rate. It is also involved in certain functions, such as reward anticipation, decision-making, impulse control. The anterior cingulate cortex can be divided based on cognitive. The ACC seems to be involved when effort is needed to carry out a task. On a cellular level, the ACC is unique in its abundance of specialized neurons called spindle cells and these cells are a relatively recent occurrence in evolutionary terms and contribute to this brain regions emphasis on addressing difficult problems, as well as the pathologies related to the ACC. A typical task that activates the ACC involves eliciting some form of conflict within the participant that can result in an error. One such task is called the Eriksen flanker task and consists of an arrow pointing to the left or right, another very common conflict-inducing stimulus that activates the ACC is the Stroop task, which involves naming the color ink of words that are either congruent or incongruent. Conflict occurs because people’s reading abilities interfere with their attempt to name the word’s ink color. A variation of this task is the Counting-Stroop, during which people count either neutral stimuli or interfering stimuli by pressing a button, many studies attribute specific functions such as error detection, anticipation of tasks, attention, ) motivation, and modulation of emotional responses to the ACC. The most basic form of ACC theory states that the ACC is involved with error detection, Evidence has been derived from studies involving a Stroop task. They found that for more competitive stimuli ACC activation was greater, a similar theory poses that the ACC’s primary function is the monitoring of conflict. In Eriksen flanker task, incompatible trials produce the most conflict, upon detection of a conflict, the ACC then provides cues to other areas in the brain to cope with the conflicting control systems. Evidence from electrical studies Evidence for ACC as having an error detection function comes from observations of error-related negativity uniquely generated within the ACC upon error occurrences, a distinction has been made between an ERP following incorrect responses and a signal after subjects receive feedback after erroneous responses. No-one has clearly demonstrated that the ERN comes from the ACC, reinforcement learning ERN theory poses that there is a mismatch between actual response execution and appropriate response execution, which results in an ERN discharge. Furthermore, this theory predicts that, when the ACC receives conflicting input from control areas in the brain, varying levels of dopamine are believed to influence the optimization of this filter system by providing expectations about the outcomes of an event. The ERN, then, serves as a beacon to highlight the violation of an expectation, research on the occurrence of the feedback ERN shows evidence that this potential has larger amplitudes when violations of expectancy are large. In other words, if an event is not likely to happen, other studies have examined whether the ERN is elicited by varying the cost of an error and the evaluation of a response

5.
Homeostasis
–
Each of these variables is controlled by a separate “homeostat”, which, together, maintain life. The concept was described by French physiologist Claude Bernard in 1865, the term cybernetics is applied to technological control systems such as thermostats, which function as homeostats, but is often defined much more broadly than the biological term homeostasis. The word homeostasis uses combining forms of homeo- and -stasis, New Latin from Greek, ὅμοιος homoios, similar and στάσις stasis, standing still, yielding the idea of staying the same. The conceptual origins of homeostasis reach back to the ancient Greek concepts of balance, harmony, equilibrium, following these hypotheses, Hippocrates compared health to the harmonious balance of the elements, and illness and disease to the systematic disharmony of these elements. Cannon published an extrapolation from Bernards 1865 work naming his theory homeostasis, Cannon further posited that threats to homeostasis might originate from the external environment or the internal environment, and could be physical or psychological, as in emotional distress. Cannon identified these negative feedback systems and emphasized that, regardless of the nature of the threat to homeostasis, the metabolic processes of all living organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the bathing the cells in multicellular creatures. However, a great many other homeostats, encompassing many aspects of human physiology, if an entity is homeostatically controlled it does not imply that its value is necessarily absolutely steady in health. Core body temperature is, for instance, regulated by a homeostat with temperature sensors in, amongst others, however the set point of the regulator is regularly reset. For instance, core temperature in humans varies during the course of the day, with the lowest temperatures occurring at night. The temperature regulators set point is readjusted in adult women at the start of the phase of the menstrual cycle. The temperature regulators set point is reset during infections to produce a fever, Homeostasis does not govern every activity in the body. For instance the signal from the sensor to the effector is, of necessity, highly variable in order to information about the direction. Similarly the effector’s response needs to be adjustable to reverse the error – in fact it should be very nearly in proportion to the error that is threatening the internal environment. The sensors send messages via sensory nerves to the medulla oblongata of the brain indicating whether the pressure has fallen or risen. One of the effector organs is the heart rate is stimulated to rise when the arterial blood pressure falls. Thus the heart rate is not homeostatically controlled, but is one of effector responses to errors in the blood pressure. Another example is the rate of sweating, the blood urea concentration is an example

6.
Self-awareness
–
Self-awareness is the capacity for introspection and the ability to recognize oneself as an individual separate from the environment and other individuals. It is not to be confused with consciousness in the sense of qualia, while consciousness is a term given to being aware of ones environment and body and lifestyle, self-awareness is the recognition of that awareness. There are questions regarding what part of the brain allows us to be self-aware, Ramachandran has speculated that mirror neurons may provide the neurological basis of human self-awareness. In an essay written for the Edge Foundation in 2009 Ramachandran gave the explanation of his theory. This could be the basis of introspection, and of the reciprocity of self awareness. There is obviously a chicken-or-egg question here as to which evolved first, the main point is that the two co-evolved, mutually enriching each other to create the mature representation of self that characterizes modern humans. Studies have been done mainly on primates to test if self-awareness is present, apes, monkeys, elephants, and dolphins have been studied most frequently. The most relevant studies to this day that represent self-awareness in animals have been done on chimpanzees, dolphins, self-awareness in animals is tested through mirror self recognition. The ‘Red Spot Technique’ created and experimented by Gordon Gallup studies self-awareness in animals, in this technique, a red odorless spot is placed on an anesthetized primates forehead. The spot is placed on the forehead so that it can only be seen through a mirror, once the individual awakens, independent movements toward the spot after seeing their reflection in a mirror are observed. Animals that can recognize themselves in mirrors can conceive of themselves, Three elephants were exposed to large mirrors where experimenters studied the reaction when they saw their reflection. These elephants were given the mark test in order to see whether they were aware of what they were looking at. This visible mark was applied on the elephants and the researchers reported a large progress with self-awareness, the elephants shared this success rate with other animals such as monkeys and dolphins. Dolphins were put to a similar test and achieved the same results, diana Reiss, a psycho-biologist at the New York Aquarium discovered that bottlenose dolphins can recognize themselves in mirrors. Researchers also used the mark test or mirror test to study the magpies self-awareness, as a majority of birds are blind below the beak, Prior and colleagues marked the birds’ neck with three different colors, red, yellow and a black imitation, as magpies are originally black. When placed in front of a mirror, the birds with the red and yellow spots began scratching at their necks, during one trial with a mirror and a mark, three out of the five magpies showed a minimum of one example of self-directed behavior. The magpies explored the mirror by moving toward it and looking behind it, one of the magpies, Harvey, during several trials would pick up objects, pose, do some wing-flapping, all in front of the mirror with the objects in his beak. This represents a sense of self-awareness, knowing what is going on within himself, a few slight occurrences of behavior towards the magpies own body happened in the trial with the black mark and the mirror

7.
Organ (anatomy)
–
In biology, an organ or viscus is a collection of tissues joined in a structural unit to serve a common function. In anatomy, a viscus is an organ, and viscera is the plural form. Organs are composed of main tissue, parenchyma, and sporadic tissues, the main tissue is that which is unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, and connective tissues. The main tissues that make up an organ tend to have common embryologic origins, functionally related organs often cooperate to form whole organ systems. Organs exist in all biological organisms, in particular they are not restricted to animals. In single-cell organisms like bacteria, the analogue of an organ is called organelle. A hollow organ is an organ that forms a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity. Two or more organs working together in the execution of a specific body function form an organ system, the functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via an organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system, the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Mammals such as humans have a variety of organ systems and these specific systems are also widely studied in human anatomy. Cardiovascular system, pumping and channeling blood to and from the body and lungs with heart, digestive system, digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum and anus. Excretory system, kidneys, ureters, bladder and urethra involved in balance, electrolyte balance. Integumentary system, skin, hair and nails, nervous system, collecting, transferring and processing information with brain, spinal cord and nerves. Reproductive system, the sex organs, such as ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, prostate, respiratory system, the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm. Skeletal system, structural support and protection with bones, cartilage, ligaments, the organ level of organisation in animals can be first detected in flatworms and the more advanced phyla. The less-advanced taxa do not show consolidation of their tissues into organs, the study of plant organs is referred to as plant morphology, rather than anatomy, as in animal systems. Organs of plants can be divided into vegetative and reproductive, vegetative plant organs are roots, stems, and leaves

8.
Spinothalamic tract
–
The spinothalamic tract is a sensory pathway from the skin to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the cortex of the postcentral gyrus. The spinothalamic tract consists of two adjacent pathways, anterior and lateral, the anterior spinothalamic tract carries information about crude touch. The lateral spinothalamic tract conveys pain and temperature, in the spinal cord, the spinothalamic tract has somatotopic organization. This is the organization of its cervical, thoracic, lumbar, and sacral components. The pathway decussates at the level of the cord, rather than in the brainstem like the posterior column-medial lemniscus pathway. There are two parts of the spinothalamic tract, The lateral spinothalamic tract transmits pain and temperature. The anterior spinothalamic tract transmits crude touch and firm pressure, the spinothalamic tract, like the dorsal column-medial lemniscus tract, uses three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex. These secondary neurons are called tract cells, the axons of the tract cells cross over to the other side of the spinal cord via the anterior white commissure, and to the anterolateral corner of the spinal cord. Decussation usually occurs 1-2 spinal nerve segments above the point of entry, the axons travel up the length of the spinal cord into the brainstem, specifically the rostral ventromedial medulla. Traveling up the brainstem, the tract moves dorsally, the neurons ultimately synapse with third-order neurons in several nuclei of the thalamus—including the medial dorsal, ventral posterior lateral, and ventral posterior medial nuclei. From there, signals go to the cortex, the primary somatosensory cortex. The types of information transmitted via the spinothalamic tract are described as affective sensation. This means that the sensation is accompanied by a compulsion to act, for instance, an itch is accompanied by a need to scratch, and a painful stimulus makes us want to withdraw from the pain. There are two sub-systems identified, Direct Indirect, in the nervous system, the anterolateral system is an ascending pathway that conveys pain, temperature, and crude touch from the periphery to the brain. This fact aids in determining whether a lesion is in the brain or the spinal cord, with lesions in the brain stem or higher, deficits of pain perception, touch sensation, and proprioception are all contralateral to the lesion. With spinal cord lesions, however, the deficit in perception is contralateral to the lesion. Unilateral lesions usually cause contralateral anaesthesia, anaesthesia will normally begin 1-2 segments below the level of lesion, affecting all caudal body areas

9.
General visceral afferent fibers
–
The general visceral afferent fibers conduct sensory impulses from the viscera, glands, and blood vessels to the central nervous system. They are considered to be part of the nervous system. However, unlike the efferent fibers of the nervous system. GVA create referred pain by activating general somatic afferent fibers where the two meet in the grey column. The cranial nerves that contain GVA fibers include the facial nerve, the glossopharyngeal nerve, in the abdomen, general visceral afferent fibers usually accompany sympathetic efferent fibers. The only GVA nerves in the abdomen that do not follow the pathway are those that innervate structures in the distal half of the sigmoid colon. These afferent fibers, instead, follow the path of parasympathetic efferent fibers back to the vertebral column, the course of GVA fibers from organs in the pelvis, in general, depends on the organs position relative to the pelvic pain line. Pain from the fibers is less likely to be consciously experienced. Afferent nerve General somatic afferent fibers General visceral efferent fibers Referred pain

10.
Respiratory system
–
The respiratory system is a biological system consisting of specific organs and structures used for the process of respiration in an organism. The respiratory system is involved in the intake and exchange of oxygen, in air-breathing vertebrates like human beings, respiration takes place in the respiratory organs called lungs. In humans and other mammals, the features of the respiratory system include trachea, bronchi, bronchioles, lungs. Molecules of oxygen and carbon dioxide are exchanged, by diffusion. This exchange process occurs in the alveoli in the lungs, in fish and many invertebrates, respiration takes place through the gills. Other animals, such as insects, have respiratory systems with very simple anatomical features, plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes features such as holes on the undersides of leaves known as stomata. The elephant is the animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of connective tissue and joined to each other via loose connective tissue. The respiratory system of birds differs significantly from that found in mammals, the lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli, the anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however, reptiles do not possess a diaphragm, thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration, both the lungs and the skin serve as respiratory organs in amphibians. The ventilation of the lungs in amphibians uses positive pressure ventilation, muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils. While the lungs are of importance to breathing control, the skins unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water. In most fish, respiration takes place through gills, lungfish, however, do possess one or two lungs. The labyrinth fish have developed an organ that allows them to take advantage of the oxygen of the air. Some species of crab use an organ called a branchiostegal lung

11.
Gastrointestinal tract
–
Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. A tract is a collection of related anatomic structures or a series of connected body organs, the mouth, oesophagus, stomach, and intestines are part of the human alimentary canal. All bilaterians have a gastrointestinal tract, also called a gut or an alimentary canal and this is a tube that transfers food to the organs of digestion. In large bilaterians, the gastrointestinal tract generally also has an exit, some small bilaterians have no anus and dispose of solid wastes by other means. The gastrointestinal tract contains thousands of different bacteria in their gut flora, the human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. In contrast, the digestive system comprises the gastrointestinal tract plus the accessory organs of digestion. The tract may also be divided into foregut, midgut, and hindgut, the whole human GI tract is about nine metres long at autopsy. The GI tract releases hormones from enzymes to help regulate the digestive process, the structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, the upper gastrointestinal tract consists of the buccal cavity, pharynx, esophagus, stomach, and duodenum. The exact demarcation between the upper and lower tracts is the muscle of the duodenum. Upon dissection, the duodenum may appear to be an organ, but it is divided into four segments based upon function, location. The four segments of the duodenum are as follows, bulb, descending, horizontal, the suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm. The suspensory muscle is an important anatomical landmark which shows the division between the duodenum and the jejunum, the first and second parts of the small intestine. This is a muscle which is derived from the embryonic mesoderm. The lower gastrointestinal tract includes most of the intestine and all of the large intestine. In humans, the intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the cecum, colon, rectum. The small intestine begins at the duodenum, which receives food from the stomach and it is a tubular structure, usually between 6 and 7 m long. The area of the human, adult small intestinal mucosa is about 30 m2 and its main function is to absorb the products of digestion into the bloodstream

12.
Thermoregulation
–
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, the internal thermoregulation process is one aspect of homeostasis, a state of dynamic stability in an organisms internal conditions, maintained far from thermal equilibrium with its environment. If the body is unable to maintain a temperature and it increases significantly above normal. For humans, this occurs when the body is exposed to constant temperatures of approximately 55 °C, humans may also experience lethal hyperthermia when the wet bulb temperature is sustained above 35 °C for six hours. The opposite condition, when temperature decreases below normal levels, is known as hypothermia. It was not until the introduction of thermometers that any data on the temperature of animals could be obtained. Hence it is important to identify the parts of the body that most closely reflect the temperature of the internal organs, also, for such results to be comparable, the measurements must be conducted under comparable conditions. The rectum has traditionally been considered to reflect most accurately the temperature of internal parts, or in cases of sex or species. Occasionally the temperature of the urine as it leaves the urethra may be of use in measuring body temperature, more often the temperature is taken in the mouth, axilla, ear or groin. Some animals undergo one of forms of dormancy where the thermoregulation process temporarily allows the body temperature to drop. Examples include hibernating bears and torpor in bats, thermoregulation in organisms runs along a spectrum from endothermy to ectothermy. Endotherms create most of their heat via metabolic processes, and are referred to as warm-blooded. Ectotherms use external sources of temperature to regulate their body temperatures and they are colloquially referred to as cold-blooded despite the fact that body temperatures often stay within the same temperature ranges as warm-blooded animals. Ectotherms are the opposite of endotherms when it comes to regulating internal temperatures, in ectotherms, the internal physiological sources of heat are of negligible importance, the biggest factor that enables them to maintain adequate body temperatures is due to environmental influences. Vaporization, Evaporation of sweat and other bodily fluids, convection, Increasing blood flow to body surfaces to maximize heat loss. Conduction, Losing heat by being in contact with a colder surface, for instance, Lying on cool ground. Staying wet in a river, lake or sea, radiation, releasing heat by radiating it away from the body. Convection, Climbing to higher ground up trees, ridges, rocks, entering a warm water or air current

13.
Endocrine system
–
The endocrine system is the collection of glands of an organism that secrete hormones directly into the circulatory system to be carried towards distant target organs. The phenomenon of biochemical processes serving to regulate distant tissues by means of directly into the circulatory system is called endocrine signaling. The major endocrine glands include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, the endocrine system is in contrast to the exocrine system, which secretes its hormones to the outside of the body using ducts. The endocrine system is a signal system like the nervous system, yet its effects. The endocrine systems effects are slow to initiate, and prolonged in their response, the nervous system sends information very quickly, and responses are generally short lived. In vertebrates, the hypothalamus is the control center for all endocrine systems. The field of study dealing with the system and its disorders is endocrinology. Special features of endocrine glands are, in general, their ductless nature, their vascularity, in contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow lumen. For example, the kidney secretes endocrine hormones such as erythropoietin and renin, hormones can consist of either amino acid complexes, steroids, eicosanoids, leukotrienes, or prostaglandins. A number of glands that signal each other in sequence are referred to as an axis, for example. The word endocrine derives from the Greek words ἐνδο- endo- inside, within, the pituitary gland is an endocrine gland about the size of a pea and weighing 0.5 grams in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, the pituitary is functionally connected to the hypothalamus by the median eminence via a small tube called the infundibular stem or pituitary stalk. Oxytocin and anti-diuretic hormone are not secreted in the posterior lobe, the pancreas is a mixocrine gland and it secretes both enzymes and hormones. In 1998, skeletal muscle was identified as an organ due to its now well-established role in the secretion of myokines. The use of the term myokine to describe cytokines and other peptides produced by muscle as signalling molecules was proposed in 2003, signalling molecules released by adipose tissue are referred to as adipokines. The human endocrine system consists of several systems that operate via feedback loops, several important feedback systems are mediated via the hypothalamus and pituitary. Cortisol has major effects, and dopamine has immunomodulatory functions. On the other hand, cytokines produced during inflammation activate the HPA axis at all three levels, sensible to negative feedback, moreover, cytokines stimulate hepcidin release from the liver, which is eventually responsible for the anemia of chronic disease

14.
Immune system
–
The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, a system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms. In many species, the system can be classified into subsystems, such as the innate immune system versus the adaptive immune system. In humans, the barrier, blood–cerebrospinal fluid barrier, and similar fluid–brain barriers separate the peripheral immune system from the neuroimmune system. Even simple unicellular organisms such as bacteria possess a rudimentary immune system in the form of enzymes that protect against bacteriophage infections, other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and invertebrates. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system, jawed vertebrates, including humans, have even more sophisticated defense mechanisms, including the ability to adapt over time to recognize specific pathogens more efficiently. Adaptive immunity creates immunological memory after a response to a specific pathogen. This process of acquired immunity is the basis of vaccination, disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer. Immunodeficiency occurs when the system is less active than normal. In humans, immunodeficiency can either be the result of a disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS. In contrast, autoimmunity results from an immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimotos thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, immunology covers the study of all aspects of the immune system. Immunology is a science that examines the structure and function of the immune system and it originates from medicine and early studies on the causes of immunity to disease. The earliest known reference to immunity was during the plague of Athens in 430 BC, thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without contracting the illness a second time. In the 18th century, Pierre-Louis Moreau de Maupertuis made experiments with scorpion venom and observed that certain dogs and this and other observations of acquired immunity were later exploited by Louis Pasteur in his development of vaccination and his proposed germ theory of disease. Pasteurs theory was in opposition to contemporary theories of disease. It was not until Robert Kochs 1891 proofs, for which he was awarded a Nobel Prize in 1905, viruses were confirmed as human pathogens in 1901, with the discovery of the yellow fever virus by Walter Reed. Immunology made an advance towards the end of the 19th century, through rapid developments, in the study of humoral immunity

15.
Charles Scott Sherrington
–
He received the Nobel Prize in Physiology or Medicine with Edgar Adrian, 1st Baron Adrian, in 1932 for their work on the functions of neurons. Prior to the work of Sherrington and Adrian, it was accepted that reflexes occurred as isolated activity within a reflex arc. Sherrington received the prize for showing that reflexes require integrated activation and his alternative explanation of synaptic communication between neurons helped shape our understanding of the central nervous system. However James Norton Sherrington was an ironmonger and artists colourman in Great Yarmouth, not a doctor, in the 1861 census, Charles is recorded as Charles Scott with Anne Sherrington as the head and Caleb Rose. He was brought up in this household with Caleb recorded as head in 1871, although Ann, the relationship between Charles and his childhood family is unknown. During the 1860s the whole family moved to Anglesea Road, Ipswich, Caleb Rose was noteworthy as both a classical scholar and an archaeologist. At the familys Edgehill House in Ipswich one could find a selection of paintings, books. Through Roses interest in the Norwich School of Painters, Sherrington gained a love of art and it was this environment that fostered Sherringtons academic sense of wonder. Even before matriculation, the young Sherrington had read Johannes Müllers Elements of Physiology, the book was given to him by Caleb Rose. Sherrington entered Ipswich School in 1871, Thomas Ashe, a famous English poet, worked at the school. Ashe served as an inspiration to Sherrington, the former instilling a love of classics, Rose had pushed Sherrington towards medicine. Sherrington first began to study with the Royal College of Surgeons of England and he also sought to study at Cambridge, but a bank failure had devastated the familys finances. Sherrington elected to enroll at St Thomas Hospital in September 1876 as a perpetual pupil and he did so in order to allow his two younger brothers to do so ahead of him. Medical studies at St. Thomass Hospital were intertwined with studies at Gonville, Physiology was Sherringtons chosen major at Cambridge. There, he studied under the father of British physiology, Sir Michael Foster, Sherrington played football for his grammar school, and for Ipswich Town Football Club, rugby St. Thomass, was on the rowing team at Oxford. During June 1875, Sherrington passed his examination in general education at the Royal College. This preliminary exam was required for Fellowship, and also exempted him from an exam for the Membership. In April 1878, he passed his Primary Examination for the Membership of the Royal College of Surgeons, in October 1879, Sherrington entered Cambridge as a non-collegiate student

16.
Proprioception
–
In humans, it is provided by proprioceptors in skeletal striated muscles and tendons and the fibrous capsules in joints. It is distinguished from exteroception, by which one perceives the world, and interoception, by which one perceives pain, hunger, etc. The brain integrates information from proprioception and from the system into its overall sense of body position, movement. The position-movement sensation was originally described in 1557 by Julius Caesar Scaliger as a sense of locomotion, much later, in 1826, Charles Bell expounded the idea of a muscle sense, which is credited as one of the first descriptions of physiologic feedback mechanisms. Bells idea was that commands are carried from the brain to the muscles, in 1889, Alfred Goldscheider suggested a classification of kinaesthesia into three types, muscle, tendon, and articular sensitivity. In 1906, Charles Scott Sherrington published a work that introduced the terms proprioception, interoception. The exteroceptors are the organs that provide information originating outside the body, such as the eyes, ears, mouth, the interoceptors provide information about the internal organs, and the proprioceptors provide information about movement derived from muscular, tendon, and articular sources. Primary endings of muscle spindles respond to the size of a length change and its speed. Secondary endings of muscle spindles detect changes in length. Essentially, muscle spindles are stretch receptors, a major component of proprioception is joint position sense, which is determined by measuring the accuracy of joint–angle replication. These involve an individuals ability to perceive the position of a joint without the aid of vision, often it is assumed that the ability of one of these aspects will be related to another, however, experimental evidence suggests there is no strong relation between these two aspects. This suggests that while these components may well be related in a cognitive manner, more recent work into the mechanism of ankle sprains suggests that the role of reflexes may be more limited due to their long latencies, as ankle sprain events occur in perhaps 100 ms or less. In accordance, a model has been proposed to include a component of proprioception. Kinesthesia is a key component in muscle memory and hand-eye coordination, the ability to swing a golf club or to catch a ball requires a finely tuned sense of the position of the joints. This sense needs to become automatic through training to enable a person to concentrate on other aspects of performance, the initiation of proprioception is the activation of a proprioreceptor in the periphery. There are specific receptors for this form of perception termed proprioreceptors, just as there are specific receptors for pressure, light, temperature, sound. Proprioreceptors are sometimes known as adequate stimuli receptors, TRPN, a member of the transient receptor potential family of ion channels, has been found to be responsible for proprioception in fruit flies, nematode worms, African clawed frogs, and zebrafish. Piezo2, a cation channel, has been shown to underlie the mechanosensitivity of proprioceptors in mice

17.
Somatic nervous system
–
The somatic nervous system is the part of the peripheral nervous system associated with skeletal muscle voluntary control of body movements. The SoNS consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves, the a- of afferent and the e- of efferent correspond to the prefixes ad- and ex-. There are 43 segments of nerves in the human body, with each segment, there is a pair of sensory and motor nerves. In the body,31 segments of nerves are in the cord and 12 are in the brain stem. Besides these, thousands of association nerves are also present in the body, thus somatic nervous system consists of two parts, Spinal nerves, They are peripheral nerves that carry sensory information into and motor commands out of the spinal cord. Cranial nerves, They are the fibers that carry information into. They include smell, vision, eye, eye muscles, mouth, taste, ear, neck, shoulders, the somatic nervous system controls all voluntary muscular systems within the body, and the process of involuntary reflex arcs. The basic route of nerve signals within the efferent somatic nervous system involves a sequence begins in the upper cell bodies of motor neurons within the precentral gyrus. Stimuli from the precentral gyrus are transmitted from upper motor neurons and down the corticospinal tract, upper motor neurons release a neurotransmitter, acetylcholine, from their axon terminal knobs, which are received by nicotinic receptors of the alpha motor neurons. In turn, alpha motor neurons relay the stimulus, from there, acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors of muscles, thereby relaying the stimulus to contract muscle fibers. A reflex arc is a circuit that creates a more or less automatic link between a sensory input and a specific motor output. Reflex circuits vary in complexity—the simplest spinal reflexes are mediated by a two-element chain, of which in the body there is only one. The singular example of a monosynaptic reflex is the patellar reflex, the next simplest reflex arc is a three-element chain, beginning with sensory neurons, which activate interneurons in the spinal cord, which then activate motor neurons. In invertebrates, depending on the neurotransmitter released and the type of receptor it binds, for vertebrates, however, the response of a skeletal striated muscle fiber to a neurotransmitter – always acetylcholine – can only be excitatory. Autonomic nervous system Enteric nervous system Nervous system

18.
Autonomic nervous system
–
The autonomic nervous system is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of internal organs. This system is the mechanism in control of the fight-or-flight response. Within the brain, the nervous system is regulated by the hypothalamus. Autonomic functions include control of respiration, cardiac regulation, vasomotor activity and those are then subdivided into other areas and are also linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the stem, acts as an integrator for autonomic functions. The autonomic nervous system has two branches, the nervous system and the parasympathetic nervous system. The sympathetic nervous system is considered the fight or flight system. In many cases, both of these systems have opposite actions where one system activates a response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as excitory and inhibitory was overturned due to the many exceptions found, there are inhibitory and excitatory synapses between neurons. Although the ANS is also known as the nervous system. Most autonomous functions are involuntary but they can work in conjunction with the somatic nervous system which provides voluntary control. The autonomic nervous system is divided into the nervous system. The sympathetic division emerges from the cord in the thoracic and lumbar areas. The parasympathetic division has craniosacral “outflow”, meaning that the neurons begin at the cranial nerves, the preganglionic, or first, neuron will begin at the “outflow” and will synapse at the postganglionic, or second, neuron’s cell body. The postganglionic neuron will then synapse at the target organ, the sympathetic nervous system consists of cells with bodies in the lateral grey column from T1 to L2/3. These cell bodies are GVE neurons and are the preganglionic neurons, the parasympathetic nervous system consists of cells with bodies in one of two locations, the brainstem or the sacral spinal cord. These sensory neurons monitor the levels of carbon dioxide, oxygen and sugar in the blood, arterial pressure and they also convey the sense of taste and smell, which, unlike most functions of the ANS, is a conscious perception. Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, primary sensory neurons project onto “second order” visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract, that integrates all visceral information

19.
Skeletal muscle
–
Skeletal muscle is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the control of the somatic nervous system. Most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons, a skeletal muscle refers to multiple bundles of cells called muscle fibers. The fibres and muscles are surrounded by connective tissue layers called fasciae, Muscle fibres, or muscle cells, are formed from the fusion of developmental myoblasts in a process known as myogenesis. Muscle fibres are cylindrical, and have more than one nucleus, Muscle fibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments, repeated in units called sarcomeres, the sarcomere is responsible for the striated appearance of skeletal muscle, and forms the basic machinery necessary for muscle contraction. Connective tissue is present in all muscles as fascia, Muscle fibres are the individual contractile units within muscle. A single muscle such as the biceps contains many muscle fibres, another group of cells, the myosatellite cells are found between the basement membrane and the sarcolemma of muscle fibers. These cells are normally quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair, development Individual muscle fibers are formed during development from the fusion of several undifferentiated immature cells known as myoblasts into long, cylindrical, multi-nucleated cells. Differentiation into this state is completed before birth with the cells continuing to grow in size thereafter. Microanatomy Skeletal muscle exhibits a distinctive banding pattern when viewed under the due to the arrangement of cytoskeletal elements in the cytoplasm of the muscle fibers. The principal cytoplasmic proteins are myosin and actin which are arranged in a unit called a sarcomere. The interaction of myosin and actin is responsible for muscle contraction, every single organelle and macromolecule of a muscle fiber is arranged to ensure form meets function. The cell membrane is called the sarcolemma with the known as the sarcoplasm. In the sarcoplasm are the myofibrils, the myofibrils are long protein bundles about 1 micrometer in diameter each containing myofilaments. Pressed against the inside of the sarcolemma are the unusual flattened myonuclei, between the myofibrils are the mitochondria. While the muscle fiber does not have a smooth endoplasmic reticulum, the sarcoplasmic reticulum surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction. Periodically, it has dilated end sacs known as terminal cisternae and these cross the muscle fiber from one side to the other

20.
Smooth muscle tissue
–
Smooth muscle is an involuntary non-striated muscle. It is divided into two subgroups, the single-unit and multiunit smooth muscle, within single-unit cells, the whole bundle or sheet contracts as a syncytium. Single unit smooth muscle, however, is most common and lines blood vessels, the tract. Smooth muscle is different from skeletal muscle and cardiac muscle in terms of structure, function, regulation of contraction. Smooth muscle cells known as myocytes, have a shape and, like striated muscle, can tense. However, smooth muscle tissue tends to demonstrate greater elasticity and function within a larger length-tension curve than striated muscle and this ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. In the relaxed state, each cell is spindle-shaped, 20-500 micrometers in length, the smooth muscle is the only type of muscle without the ability to be voluntarily controlled in stressful situations. Myosin is primarily class II in smooth muscle, myosin II contains two heavy chains which constitute the head and tail domains. Each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, thus, myosin II has two heads. In smooth muscle, there is a gene that codes for the heavy chains myosin II. Also, smooth muscle may contain MHC that is not involved in contraction, myosin II also contains 4 light chains, resulting in 2 per head, weighing 20 and 17 kDa. These bind the chains in the neck region between the head and tail. The MLC20 is also known as the light chain and actively participates in muscle contraction. Two MLC20 isoforms are found in muscle, and they are encoded by different genes. The MLC17 is also known as the light chain. Its exact function is unclear, but its believed that it contributes to the stability of the myosin head along with MLC20. Two variants of MLC17 exist as a result of alternate splicing at the MLC17 gene, in the uterus, a shift in myosin expression has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle. The thin filaments that form part of the machinery are predominantly composed of α-

21.
John Newport Langley
–
Prof John Newport Langley FRSE LLD was a British physiologist. He was born in Newbury, Berkshire the son of John Langley, the local schoolmaster and he was educated at Exeter Grammar School in Devon. In 1871 he won a place at St Johns College in Cambridge University where he graduated MA before continuing multiple postgraduate studies and he spent his entire career at Cambridge University, beginning as a Demonstrator in lectures in 1875. He began lecturing in Physiology in 1884 and was awarded a professorship in 1903 and he was elected a Fellow of the Royal Society in 1883 and later its vice-president. He was made an Honorary Fellow of the Royal Society of Edinburgh in 1916, Langley is known as one of the fathers of the chemical receptor theory, and as the origin of the concept of receptive substance. In 1901, he advanced research in neurotransmitters and chemical receptors and these extracts elicited responses in tissues that were similar to those induced by nerve stimulation. He died in Cambridge on 5 November 1925, the Autonomic Nervous System Elementary Experimental Physiology A brass plaque to Langleys memory exists in Trinty College Chapel at Cambridge University. In 1902 he married Vera Kathleen Forsythe-Grant, katz, B. Archibald Vivian Hill, Dictionary of National Biography, Oxford University Press, Oxford, p.406

22.
Classical conditioning
–
Classical conditioning refers to a learning procedure in which a biologically potent stimulus is paired with a previously neutral stimulus. These basic facts, which require many qualifications, were first studied in detail by Ivan Pavlov through experiments with dogs, Classical conditioning is the basic learning process, and its neural substrates are now beginning to be understood. Classical conditioning occurs when a stimulus is paired with an unconditioned stimulus. After pairing is repeated, the organism exhibits a conditioned response to the stimulus when the conditioned stimulus is presented alone. The conditioned response is similar to the unconditioned response, but unlike the unconditioned response. Robert A. Rescorla provided a summary of this change in thinking. Despite its widespread acceptance, Rescorlas thesis may not be defensible, the best-known and most thorough early work on classical conditioning was done by Ivan Pavlov, although Edwin Twitmyer published some related findings a year earlier. During his research on the physiology of digestion in dogs, Pavlov developed a procedure that enabled him to study the processes of animals over long periods of time. He redirected the animal’s digestive fluids outside the body, where they could be measured, Pavlov noticed that his dogs began to salivate in the presence of the technician who normally fed them, rather than simply salivating in the presence of food. Pavlov called the dogs anticipatory salivation psychic secretion, putting these informal observations to an experimental test, Pavlov presented a stimulus and then gave the dog food, after a few repetitions, the dogs started to salivate in response to the stimulus. Pavlov concluded that if a stimulus in the dogs surroundings was present when the dog was given food then that stimulus could become associated with food. He called the stimulus the conditioned stimulus because its effects depend on its association with food and he called the food the unconditioned stimulus because its effects did not depend on previous experience. Likewise, the response to the CS was the conditioned response, Pavlov reported many basic facts about conditioning, for example, he found that learning occurred most rapidly when the interval between the CS and the appearance of the US was relatively short. In fact, the CR may be any new response to the previously neutral CS that can be linked to experience with the conditional relationship of CS. It was also thought that repeated pairings are necessary for conditioning to emerge, learning is fastest in forward conditioning. During forward conditioning, the onset of the CS precedes the onset of the US in order to signal that the US will follow, two common forms of forward conditioning are delay and trace conditioning. Delay conditioning, In delay conditioning the CS is presented and is overlapped by the presentation of the US, trace conditioning, During trace conditioning the CS and US do not overlap. Instead, the CS begins and ends before the US is presented, the stimulus-free period is called the trace interval

23.
Action potential
–
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of cells, called excitable cells, which include neurons, muscle cells. In other types of cells, their function is to activate intracellular processes. In muscle cells, for example, a potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin, action potentials in neurons are also known as nerve impulses or spikes, and the temporal sequence of action potentials generated by a neuron is called its spike train. A neuron that emits an action potential is often said to fire, action potentials are generated by special types of voltage-gated ion channels embedded in a cells plasma membrane. When the channels open they allow a flow of sodium ions, which changes the electrochemical gradient. This then causes more channels to open, producing an electric current across the cell membrane. The process proceeds explosively until all of the ion channels are open. The rapid influx of ions causes the polarity of the plasma membrane to reverse. As the sodium channels close, sodium ions can no longer enter the neuron, potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, in animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels, sodium-based action potentials usually last for under one millisecond, whereas calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the hand, an initial fast sodium spike provides a primer to provoke the rapid onset of a calcium spike. Nearly all cell membranes in animals, plants and fungi maintain a voltage difference between the exterior and interior of the cell, called the membrane potential. A typical voltage across a cell membrane is –70 mV. In most types of cells the membrane potential usually stays fairly constant, some types of cells, however, are electrically active in the sense that their voltages fluctuate over time

24.
Psychophysiology
–
Psychophysiology is the branch of psychology that is concerned with the physiological bases of psychological processes. Some people have difficulty distinguishing a psychophysiologist from a physiological psychologist, psychologists are interested in why we may fear spiders and physiologists may be interested in the input/output system of the amygdala. A psychophysiologist will attempt to link the two, psychophysiologists generally study the psychological/physiological link in intact human subjects. It is this perspective of studying the interface of mind and body that makes psychophysiologists most distinct, historically, most psychophysiologists tended to examine the physiological responses and organ systems innervated by the autonomic nervous system. Often, physiological psychologists examine the effects that they study in infrahuman subjects using surgical or invasive techniques and processes, psychophysiology is closely related to the field of neuroscience and social neuroscience, which primarily concerns itself with relationships between psychological events and brain responses. Psychophysiology is also related to the discipline known as psychosomatics. Psychophysiology measures exist in three domains, reports, readings, and behavior, Physiological responses also can be measured via instruments that read bodily events such as heart rate change, electrodermal activity, muscle tension, and cardiac output. These measures are beneficial because they provide accurate and perceiver-independent objective data recorded by machinery, the downsides, however, are that any physical activity or motion can alter responses, and basal levels of arousal and responsiveness can differ among individuals and even between situations. Finally, one can measure overt action or behavior, which involves the observation and recording actual actions, such as running, freezing, eye movement and these are good response measures and easy to record in animals, but they are not as frequently used in human studies. Psychophysiological measures are used to study emotion and attention responses to stimuli, during exertion. Physiological sensors have been used to detect emotions in schools and intelligent tutoring systems and it has long been recognized that emotional episodes are partly constituted by physiological responses. Early work done linking emotions to psychophysiology started with research on mapping consistent autonomic nervous system responses to emotional states. The autonomic activity produced distinguished not only positive and negative emotions, but also among negative emotions”. Some of these differences can be attributed to variables like induction technique, context of the study, or classification of stimuli, however it was also found that features of the participant could also alter ANS responses. Even supposedly discrete emotional states fail to show specificity, as such no definitive correlation can be drawn linking specific autonomic patterns to discrete emotions, causing emotion theorists to rethink classical definitions of emotions. Physiological computing represents a category of affective computing that incorporates real-time software adaption to the activity of the user. The main goal of this is to build a computer that responds to user emotion, cognition and motivation, the approach is to enable implicit and symmetrical human-computer communication by granting the software access to a representation of the users psychological status. There are several methods to represent the psychological state of the user

25.
Emotion
–
Emotion, generally speaking, is any relatively brief conscious experience characterized by intense mental activity and a high degree of pleasure or displeasure. Scientific discourse has drifted to other meanings and there is no consensus on a definition, Emotion is often intertwined with mood, temperament, personality, disposition, and motivation. In some theories, cognition is an important aspect of emotion and those acting primarily on the emotions they are feeling may seem as if they are not thinking, but mental processes are still essential, particularly in the interpretation of events. For example, the realization of our believing that we are in a dangerous situation, other theories, however, claim that emotion is separate from and can precede cognition. According to some theories, they are states of feeling that result in physical and psychological changes that influence our behavior, the physiology of emotion is closely linked to arousal of the nervous system with various states and strengths of arousal relating, apparently, to particular emotions. Emotion is also linked to behavioral tendency, extroverted people are more likely to be social and express their emotions, while introverted people are more likely to be more socially withdrawn and conceal their emotions. Emotion is often the force behind motivation, positive or negative. Nor is the emotion an entity that causes these components, Emotions involve different components, such as subjective experience, cognitive processes, expressive behavior, psychophysiological changes, and instrumental behavior. More recently, emotion is said to consist of all the components, the different components of emotion are categorized somewhat differently depending on the academic discipline. In psychology and philosophy, emotion typically includes a subjective, conscious experience characterized primarily by psychophysiological expressions, biological reactions, a similar multicomponential description of emotion is found in sociology. For example, Peggy Thoits described emotions as involving physiological components, cultural or emotional labels, expressive body actions, the numerous theories that attempt to explain the origin, neurobiology, experience, and function of emotions have only fostered more intense research on this topic. Current areas of research in the concept of emotion include the development of materials that stimulate, in addition PET scans and fMRI scans help study the affective processes in the brain. Emotions can be defined as a positive or negative experience that is associated with a pattern of physiological activity. Emotions produce different physiological, behavioral and cognitive changes, the original role of emotions was to motivate adaptive behaviors that in the past would have contributed to the survival of humans. Emotions are responses to significant internal and external events, the word emotion dates back to 1579, when it was adapted from the French word émouvoir, which means to stir up. The term emotion was introduced into academic discussion to replace passion, according to one dictionary, the earliest precursors of the word likely dates back to the very origins of language. The modern word emotion is heterogeneous In some uses of the word, on the other hand, emotion can be used to refer to states that are mild and to states that are not directed at anything. One line of research looks at the meaning of the word emotion in everyday language

A sense is a physiological capacity of organisms that provides data for perception. The senses and their operation, …

Five senses and the respective sensory organs inherent among Homo sapiens

An allegory of five senses. Still Life by Pieter Claesz, 1623. The painting illustrates the senses through musical instruments, a compass, a book, food and drink, a mirror, incense and an open perfume bottle. The tortoise may be an illustration of touch or an allusion to the opposite (the tortoise isolating in its shell).

Fig. 11 A highly diagrammatic illustration of the process of gas exchange in the mammalian lungs, emphasizing the differences between the gas compositions of the ambient air, the alveolar air (light blue) with which the pulmonary capillary blood equilibrates, and the blood gas tensions in the pulmonary arterial (blue blood entering the lung on the left) and venous blood (red blood leaving the lung on the right). All the gas tensions are in kPa. To convert to mm Hg, multiply by 7.5.

Fig. 10 A histological cross-section through an alveolar wall showing the layers through which the gases have to move between the blood plasma and the alveolar air. The dark blue objects are the nuclei of the capillary endothelial and alveolar type I epithelial cells (or type 1 pneumocytes). The two red objects labeled "RBC" are red blood cells in the pulmonary capillary blood.

Relationship of major animal lineages with indication of how long ago these animals shared a common ancestor. On the left, important organs are shown, which allows us to determine how long ago these may have evolved.

The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils.

In politics, humanitarian aid, and social science, hunger is a condition in which a person, for a sustained period, is …

The FAO's food price index reflects changes in the average international price of food. The sharp rise in 2007/08 caused a global food crisis, with food riots in dozens of countries, and pushed well over a hundred million into extreme hunger. The sharp rise in 2010/11 contributed to the Arab Spring.

Function of T helper cells: Antigen-presenting cells (APCs) present antigen on their Class II MHC molecules (MHC2). Helper T cells recognize these, with the help of their expression of CD4 co-receptor (CD4+). The activation of a resting helper T cell causes it to release cytokines and other stimulatory signals (green arrows) that stimulate the activity of macrophages, killer T cells and B cells, the latter producing antibodies. The stimulation of B cells and macrophages succeeds a proliferation of T helper cells.

The time-course of an immune response begins with the initial pathogen encounter, (or initial vaccination) and leads to the formation and maintenance of active immunological memory.